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PRI's Environmental News Magazine

Soy and Prostrate Cancer

Air Date: Week of December 3, 1999

New research shows that diets rich in soy may help combat prostate cancer. Host Steve Curwood discusses the latest findings with Janet Raloff, senior editor at Science News and Living On Earth’s science correspondent.

Transcript

CURWOOD: Joining me now is Janet Raloff, senior editor at Science News and Living on Earth's science correspondent. Hi, Janet.

RALOFF: Hello, Steve.

CURWOOD: Janet, there's news of some possible health effects from that high-protein bean plant called soy, which is made into everything from infant formula to tofu. In two recent studies, scientists have reported that Asian men with a diet rich in soy die less often from prostate cancer than men in western nations, even though both groups have the same incidence of the disease. Janet, what's behind these two new animal studies that could explain this difference?

RALOFF: What they're finding is, the major difference is that when you give animals some foods that are rich in plant estrogens, and we're talking here, like soy or rye, that these animals develop cancers that grow more slowly and also ones that spread less throughout the body.

CURWOOD: So, tell me about these plant estrogens. What exactly do they do?

RALOFF: Well, in one study, they seem to prevent the development of blood vessels that come to feed a new tumor. And essentially, they starve these tumors, which may explain the slow growth. In the other, they seem to find that these particular kinds of foods, like the soy and the rye, seem to be able to cause cells of the cancer to undergo what they call a programmed cell death, a natural death. Something they don't ordinarily see in a cancer. Cancers grow with uncontrolled proliferation, and that's because they're not normally undergoing this programmed cell death.

CURWOOD: Now, why do you think plant estrogens work to help protect against cancer, when human and other animal estrogens don't?

RALOFF: In a sense, the body was made to have various kinds of gene actions unlocked by these hormones, estrogens. But these plant ones aren't quite the same, and they're almost like a skeleton key. So they don't unlock the normal gene action in quite the same way, and sometimes not at all. They also seem to be more effective in different tissues than your ordinary animal estrogen would.

CURWOOD: Now, I find this fascinating, that somehow soy plants would protect against cancer. Nature must have somehow designed this, right? I mean, how did scientists find plant estrogens to begin with, anyway?

RALOFF: Well, they actually found them because they were shutting down reproduction in some livestock in Australia, and then later on in other places as well. Turns out that the clover these animals were grazing on, if they got too much of it, it actually just shut down reproduction altogether. When they tried to find out why, they found out the compounds in the clover mimicked, and in fact even resembled structurally, natural human estrogens. Now, they're wondering whether these plants develop them, in a sense, to protect themselves against grazing, so they didn't get grazed out of existence.

CURWOOD: (Laughs) Birth control for cows, huh?

RALOFF: Absolutely.

CURWOOD: What are some of the other plants that have these estrogens, aside from soy?

RALOFF: Well, you can find them in lots of nuts, in whole grains, including wheat, rye, and corn, even rice. You can find them in some fruits, like cherries and apples. You can find them in carrots and potatoes. And ginseng. Even coffee and tea.

CURWOOD: That's a long list. But soy's the big one, huh?

RALOFF: Well, yeah. Biggest bang for the buck. There's an awful lot of these things in soy, and soy is so easy to incorporate in the diet.

CURWOOD: Now, this is not a cooking show, Janet. But do you have a favorite recipe for soy, for someone who might want to eat this stuff to try to combat prostate cancer?

RALOFF: My daughter's favorite is our chocolate mousse tofu pie. It's almost exclusively tofu, to which you blend in some melted chocolate chips, just a little bit of sugar, and you put it into a graham cracker or a chocolate cookie crust. Let it sit in the refrigerator to chill. And I defy anyone to realize they're eating rich soy. It's wonderful.

CURWOOD: (Laughs) Well, thank you. Janet Raloff is senior editor of Science News and Living on Earth's science correspondent. Good talking with you.

RALOFF: Bye, Steve.

 

 

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